This invention relates to a system for monitoring intracranial pressure and intracranial bloodflow during medical observation or surgical activity taking place within the cranium.
The increasing recognition of the need for immediate attention to be given injured patients by specialists in traumatic medicine has generated a concomitant need for apparatus and procedures which provide the medical personnel with reliable information concerning the body-function parameters of the injured patient. In particular, an injury occurring on or within the cranium of an individual requires information-gathering techniques to be immediately utilized. At present, the use of intracranial pressure monitoring apparatus is recognized as necessary to provide the medical personnel information concerning increases or drops in pressure within the confines of the cranium. This measurement is found to be important since an increase in fluid pressure within the skull manifests itself as a reduction in bloodflow to the brain of the injured patient. In practice, it is customary to use a transducer which is inserted through a hole intentionally formed in the cranium. The transducer pressure serves as a sensor and is electricially similar to the well-known strain gauge bridge configuration and generates an electrical signal in response to fluid pressure changes. The output of the transducer is supplied to a monitoring device which gives a visual display of pressure variations in the cranium.
An additional monitoring device has been provided to the medical team administering to trauma patients which utilizes thermal diffusion techniques to aid in the determination of bloodflow in body tissue and is particularly well-suited for intracranial measurements. One such device suitable for use in determining cortical bloodflow is the thermal diffusion bloodflow probe set forth in my U.S. Pat. No. 4,354,504. This probe is intended to be utilized during surgery when the cranium is opened and the dura is held in place with retractors so as to enable the probe to be placed in contact with brain tissue. The probe then generates an electrical signal indicative of the bloodflow in that region of the brain.
Recently, the interaction of intracranial pressure and intracranial bloodflow has received increasing attention from medical personnel operating in this field. There is an inverse relationship between intracranial pressure and the bloodflow therein since the cranium or skull has a finite volume. The increase in pressure of fluid surrounding the brain coupled with the swelling of the brain itself has been found to result in reduced bloodflow through the network of blood vessels in the brain. Historical data indicates that as the intracranial pressure of an individual increases significantly, the patient is not likely to do well. Consequently, increasing attention is directed to the interaction between blood pressure, bloodflow and intracranial pressure.
An autoregulation system exists within the human body to cause blood vessels to dilate and thereby increase capacity to carry blood. However, it is believed that as intracranial pressure increases to a high level or increases at a very rapid rate, then the vessels are unable to either dilate further or rapidly enough. Consequently, the bloodflow in the brain is diminished as pressure increases. It is believed that the autoregulation system works for a while during initial pressure increases, thus lulling the medical observer into the situation where they believe the conditions to be following the predicted pattern. When the point is reached that the autoregulation system cannot handle the results of increasing intracranial pressure, external pharmacological agents must be introduced into the body in an attempt to stimulate bloodflow by the intentional increasing of blood pressure in the body.
Accordingly, the present invention has as a primary object the provision of a system for sensing intracranial bloodflow and pressures, monitoring these quantities for irregularities or dangerous conditions and providing an external display of information promptly to enable the medical personnel to react accordingly. A further object is the provision of a system in which a controlling function directed to the modification of fluids being introduced into the vascular system of the patient takes place without the need for independent action by the attendant personnel. Also, the system provides for interaction between the intracranial pressure monitor and the cranial bloodflow monitor so as to automatically adjust the predetermined lower limit for bloodflow in response to a high rate of increase as well as a high level of intracranial pressure.